The present invention generally relates to sputtering apparatuses.
Recently, there has been increasing interest in organic EL element as a display device.
FIG. 12 is a schematic cross-sectional view for illustrating the structure of an organic EL device 201.
This organic EL device 201 has a lower electrode 214, organic layers 217, 218, and an upper electrode 219 laminated in this order on a substrate 211; and light emission occurs within the organic layers 217, 218 or at the interface between the organic layers 217, 218 if a voltage is applied to between the upper electrode 219 and the lower electrode 214. If the upper electrode 219 is composed of a transparent conductive film (such as, an ITO film (indium tin oxide film)), the luminescent light is transmitted through the upper electrode 219 and emitted to the outside.
As the method of forming the upper electrode 219 as described above, a vapor deposition method is mainly used.
In the vapor deposition method, particles emitted from a deposition source due to the sublimation or evaporation are neutral particles with a low energy (approximately several eV), so there is the advantage of forming an excellent interface without damaging the organic layers 217, 218 when forming a protective film of the upper electrode 219 and organic EL device.
However, since films formed with the vapor deposition method have poor adhesion to the organic layer, problems occur, such problems including the generation of dark spots and the exfoliation of electrodes due to the long-term drive. Moreover, from the viewpoint of productivity, the vapor deposition method has problems, including the difficulty in ensuring a film thickness distribution in a large area due to a point evaporation source, and a short maintenance cycle due to the deterioration of an evaporation boat and the difficulty in continuously supplying evaporation materials.
As ways to solve the above-described problems, the way of a sputtering method has been proposed. However, in a parallel plate type sputtering method in which an object to be film-formed is made to face the surface of a target, when an aluminum upper electrode is formed on the organic layer, problems occur in the driving test of the organic EL devices. Such problems include luminescence starting voltage becoming extremely high or no light being emitted. These problems occur because in the sputtering method, the charged particles (Ar ions, secondary electrons, recoil Ar) in plasma and the sputtered particles with a high kinetic energy are irradiated upon the organic layer, thereby destroying the interface between the organic layers and thus failing to favorably inject electrons.
Consequently, also in the conventional art, countermeasures have been sought and a sputtering apparatus 110 as shown in FIG. 13 has been proposed.
This sputtering apparatus 110 has a vacuum chamber 111; and in the vacuum chamber 111, two targets 121a, 121b are opposingly arranged in parallel while the rear surfaces thereof are attached to backing plates 122a, 122b, respectively; and the front surfaces thereof are spaced from each other by a certain distance.
Magnetic field forming devices 115a, 115b are arranged on the rear surfaces of the backing plates 122a, 122b, respectively. The magnetic field forming devices 115a, 115b are constructed by attaching ring-shaped magnets 123a, 123b to yokes 129a, 129b, respectively.
Each of the magnets 123a, 123b is arranged with one of the magnetic poles being faced toward the target 121a, 121b and the other magnetic pole being faced toward the direction opposite to the target and in two magnets 123a, 123b the magnetic poles with different polarities are faced toward the targets 121a, 121b, respectively.
In short, since one magnet 123a faces the N pole toward the target 121a and the other magnet 123b faces the S pole toward the target 121b, magnetic lines of force 131 are generated between the two magnets 123a, 123b. Since the magnets 123a, 123b are ring-shaped, the magnetic lines of force generated between the magnets 123a, 123b become cylindrical (FIG. 14).
When the inside of the vacuum chamber 111 is evacuated by a vacuum evacuating system 116 and a sputtering gas is introduced from a gas introduction system 117 and voltage is applied to the targets 121a, 121b, a plasma of the sputtering gas is generated in a space sandwiched between the targets 121a, 121b; and thus, the surfaces of the targets 121a, 121b are sputtered.
An object to be film-formed 113 is arranged lateral to the space sandwiched between the targets 121a, 121b, and a thin film is formed on the surface of the object to be film-formed 113 by the sputtered particles that are diagonally emitted from the targets 121a, 121b and are discharged into the vacuum chamber 111.
In this sputtering apparatus 110, the space in which the targets 121a, 121b face each other is surrounded by the cylindrical magnetic lines of force 131 formed in between two magnets 123a, 123b, and the plasma is confined by the magnetic lines of force 131; and for this reason the plasma does not leak out to the object to be film-formed 113. Accordingly, the object to be film-formed 113 does not get exposed to the charged particles in the plasma; and thus, the organic thin film exposed on the surface of the object to be film-formed 113 is not damaged.
However, in the above-described sputtering apparatus 110, a phenomenon occurs whereby the center portions of the targets 121a, 121b are eroded deeper than their edge portions by sputtering.
Since an abnormal discharge occurs if the targets 121a, 121b are eroded so deep that the backing plates 122a, 122b at the rear surface side of the targets get exposed, the targets 121a, 121b are replaced before the backing plates 122a, 122b get exposed.
If only a part of the targets 121a, 121b is deeply eroded, the targets 121a, 121b have to be replaced even if the decreased amount of the film thickness in the other part is small; and thus, the usage efficiency of the target in the conventional sputtering apparatus 110 is poor.
See, Patent Documents No. JPA 11-162652 and JPA 2005-032618.